If I were uber rich that would be my goal. More than all the houses, the planes and exotic cars, the sports franchises, having a foundation with the means to do lasting good on a globally significant scale and leaving a legacy rather than just an estate would be so fulfilling. Well it would for me anyway.
Not a big Microsoft fan, but I absolutely admire Gates for his foundation's work. Given it was MS that bought Minecraft I'm sure Bill could give him some pointers.